This research will involve studies of the manner(s) in which mitochondria of mammalian cells acquire two important hemoprotein components of their respiratory system: cytochrome oxidase and cytochrome c. Rats pretreated with 3-methylcholanthrene will be used to provide an experimental system wherein the synthesis of mitochondrial proteins is enhanced. Measurements of incorporation of precursors into, and of net synthesis of, cytochrome oxidase will be facilitated by use of a rabbit serum antibody to that entity. The nature and extent of the cooperative actions by the endoplasmic reticulum (ER) and the mitochondria requisite for the appearance of functional cytochrome c and cytochrome oxidase within the mitochondria will be determined. Insofar as cytochrome c is concerned, the exact nature of the precursor that is manufactured by the ER and the mechanisms of its transfer to the mitochondria and of its conversion to functional cytochrome c will be determined. In regard to cytochrome oxidase, the nature and extent of contributions of both protein and nonprotein components by the ER to synthesis will be determined. Upon development of suitable methods for study of synthesis of the hemoproteins, the processes will be characterized as completely as possible. The half-lives of total mitochondrial proteins, inner and outer mitochondrial membrane proteins, cytochrome c and cytochrome oxidase will be assessed. This knowledge of the processes of synthesis and the relative stabilities of a soluble component (cytochrome c) and an insoluble component (cytochrome oxidase) of the inner mitochondrial membrane will provide an important contribution to an understanding of the mechanisms of mitochondrial biogenesis.